Some conventional semiconductor fabrication processes, for example anneal processes, may require a process chamber be maintained at high temperatures and low pressure to perform the process. However, the inventors have observed that performing a process at such temperature and pressure may undesirably cause sublimation of materials or diffusion of dopants from the substrate. For example, when annealing silicon-containing substrates, oxygen within the process chamber (e.g., moisture, residual material from previous processes performed in the process chamber, leakage from first gas supply, or the like) may attack the surfaces of the substrate, forming silicon oxide. The silicon oxide may then condense on surfaces of the process chamber, for example, side walls, reflector plates, pyrometers, or the like. In order to preserve process consistency, the process chamber requires periodic maintenance to remove the condensed materials, thus reducing processing efficiency and throughput.
Typically, in process chambers such as rapid thermal process (RTP) chambers, a gas having a low concentration of oxygen may be flowed to the front side of the substrate to prevent the aforementioned sublimation. However, such conventional process chambers typically have a large difference in gas conductance between the front side of a substrate and a back side of the substrate. This difference in gas conductance leads to an inadequate amount of oxygen reaching the back side of the substrate to prevent sublimation of materials from the back side of the substrate.
Therefore, the inventors have provided improved methods and apparatus for processing a substrate.